1. Field of the Invention
Exemplary embodiments of the present invention relate to an electro-magnetic tomography, and more particularly, to an electro-magnetic tomography capable of accurately measuring a phase of an electro-magnetic receive signal using modulated signals in a tomography using a measured electro-magnetic signal.
2. Description of Related Art
An electro-magnetic tomography is a technology that transmits an electro-magnetic wave from one point for electro-magnetic tomography, measures the transmission electro-magnetic wave through an object at a receiving point, and analyzes a phase and amplitude of the measured electro-magnetic wave, thereby acquiring a tomography image of an object.
FIG. 1 is a diagram for describing a phase measurement process in an electro-magnetic tomography in accordance with the related art.
As illustrated in FIG. 1, an electro-magnetic tomography system is configured to include a signal generator 10, a transmitter antenna 11, a receiver antenna 12, and a phase and amplitude detector 13.
Generally, in the phase measurement, the signal generator 10 to generate one continuous wave signal from frequency f1 to frequency fN and propagate the generated one continuous signal through the transmitter antenna 11. Further, the signal generator 10 receives the same electro-magnetic wave propagated through the transmitter antenna from the receiver antenna and transmits the received electro-magnetic wave to the phase and amplitude detector 13. The phase and amplitude detector 13 measures the phase and amplitude by comparing the magnitude in the phase and amplitude between the continuous wave signal generated by the signal generator 10 at the transmitting side and the signal received through the receiver antenna. The tomography image is generated by applying an image reconfiguration method using the measured phase and amplitude.
FIG. 2 is a diagram for describing the phase measurement method in the electro-magnetic tomography in accordance with the related art and illustrates comparison results of period A and period B by using the above-mentioned phase measurement method of FIG. 1.
Reviewing the period A, when a wavelength of a frequency of a transmit carrier signal propagated from the transmitter antenna 11 is longer than distances d1, d2, and d3 between the transmitter antenna 11 and the receiver antennas 12, 13, and 14, if phases 18, 19, and 20 of a signal measured by setting the frequency starting points 15, 16, and 17 of the transmit carrier signal to a zero point do not exceed 180°, the amplitude and phase detector 13 can accurately measure the phases.
On the other hand, reviewing the period B, in the case of a high frequency signal in which the wavelength of the frequency of the transmit carrier signal starting the transmitter antenna 11 is shorter than the distance between the transmitter antenna 11 and the receiver antennas 12, 13, and 14, if phases 24, 25, and 26 of a signal measured by setting the frequency starting points 21, 22, and 23 of the transmit carrier signal to a zero point exceeds 180°, the amplitude and phase detector 13 cannot recognize the signal exceeding 180° and thus, has a problem of measurement phase ambiguity that does not accurately measure the phase in a 180°×N times+α (a residual value within 180°) type and outputs the phase in only the α (a residual value within) 180° type.
Due to the above problem, in the case of a high frequency signal in which the wavelength of the frequency of the transmit electro-magnetic wave is shorter than the distance between the transmitter antenna 11 and the receiver antennas 12, 13, and 14, the image reconfiguration calculation cannot be accurately performed and thus, the accurate image cannot be extracted at the time of the tomography.